Transmission method and radio system

Abstract

The invention relates to a data transmission method and a radio system implementing method. A transmitter has at least two modulation methods by which it can modulate a signal. One or more demodulators ( 106 ) of the receiver demodulates the received signal in a manner which corresponds to each modulation method used. The modulation method used for the signal is inferred in a reference block ( 110 ) from the impulse response estimate. The signal according to the inferred modulation method is detected in a detector ( 114 ).

What is claimed is:  
     
       1. A data transmission method used in a radio system comprising at least a base station and a terminal which include a transmitter and a receiver for signal transmission and reception, in which data transmission method a signal is transmitted in bursts which comprise a training sequence ( 404 ,  412 ), it is possible to use at least two predetermined modulation methods for a signal that is to be transmitted, and the modulation method used is interchangeable to another predetermined modulation method, characterized in that 
       when the transmitted signal is received it is demodulated in the manner corresponding to each modulation method;  
       an impulse response estimate which corresponds to each modulation method used is formed for the received signal; and  
       the modulation method which is used for the transmitted signal is inferred from the impulse response estimate and the signal according to the inferred modulation method is selected to be detected.  
     
     
       2. A data transmission method used in a radio system comprising at least a base station and a terminal which include a transmitter and a receiver for signal transmission and reception, in which data transmission method a signal is transmitted in bursts which comprise a training sequence ( 404 ,  412 ), it is possible to use at least two predetermined modulation methods for a signal that is to be transmitted, and the modulation method used is interchangeable to another predetermined modulation method, characterized in that 
       when the transmitted signal is received it is demodulated by only one demodulation method;  
       an impulse response estimate which corresponds to each modulation method used is formed for the received signal; and  
       the modulation method used for the transmitted signal is inferred from the impulse response estimate and the signal is detected.  
     
     
       3. A method as claimed in  claim 2 , characterized in that a detection mode for detecting the signal is selected according to the modulation method used. 
     
     
       4. A method as claimed in  claim 1 , characterized in that the modulation method is inferred from the impulse response by means of the principle of maximum likelihood. 
     
     
       5. A method as claimed in  claim 1 , characterized in that the training sequences ( 404 ,  412 ) are overlapped in time domain in a burst transmitted by each modulation method. 
     
     
       6. A method as claimed in  claim 5 , characterized in that the training sequences ( 404 ,  412 ) modulated by different modulation methods and overlapped in time domain are mutually substantially orthogonal, whereby separating different modulation methods becomes easier in reception. 
     
     
       7. A method as claimed in  claim 1 , characterized in that the modulation method is inferred from the impulse response by means of the energy of the impulse response, a signal-to-noise ratio or a signal-to-interference ratio. 
     
     
       8. A method as claimed in  claim 1 , characterized in that the received signal is detected at least partly and the detected portion is utilized when the modulation method of the received signal is inferred. 
     
     
       9. A method as claimed in  claim 1 , characterized in that modulation methods which operate at a different data transmission rate are used. 
     
     
       10. A method as claimed in  claim 9 , characterized in that when the GSM radio system is used and when a FACCH signal is transmitted, the FACCH signal is always transmitted at a lower data transmission rate, whereby no FACCH bits are needed in the bursts ( 412 ) which operate at higher data transmission rates. 
     
     
       11. A method as claimed in  claim 9 , characterized in that two modulation methods are used, of which one is DBCPM enabling higher data transmission rate and the other is GMSK. 
     
     
       12. A radio system comprising at least a base station and a terminal which include a transmitter and a receiver for signal transmission and reception, in which radio system the transmitter is arranged to transmit a signal in bursts which comprise a training sequence ( 404 ,  412 ), it is possible to use at least two predetermined modulation methods for a signal that is to be transmitted, and the modulation method used is interchangeable to another predetermined modulation method, characterized in that the receiver comprises 
       at least a demodulator ( 106 ,  206 ) for demodulating the received signal in the manner corresponding to each modulation method used;  
       means ( 108 ) for forming an impulse response estimate which corresponds to each modulation method used;  
       means ( 112 ) for selecting a demodulated signal for the detector ( 114 );  
       means ( 110 ) for inferring from the impulse response estimate the modulation method which is used for the transmitted signal and for controlling the means ( 112 ) to select for the detector ( 114 ) a signal which is correspondingly demodulated.  
     
     
       13. A radio system comprising at least a base station and a terminal which include a transmitter and a receiver for signal transmission and reception, in which radio system the transmitter is arranged to transmit a signal in bursts which comprise a training sequence ( 404 ,  412 ), it is possible to use at least two predetermined modulation methods for a signal that is to be transmitted, and the modulation method which is used is interchangeable to another predetermined modulation method, characterized in that the receiver comprises 
       only one demodulator ( 206 );  
       means ( 208 ) for forming an impulse response estimate which corresponds to each modulation method used;  
       means ( 210 ) for inferring from the impulse response estimate the modulation method which is used for the transmitted signal;  
       a detector ( 212 ) for detecting the signal, and  
       the transmitter is arranged to use modulation methods which the one demodulator ( 206 ) of the receiver is able to demodulate.  
     
     
       14. A radio system as claimed in  claim 12 , characterized in that the means ( 110 ,  210 ) for inferring the modulation method from the impulse response are arranged to use the principle of maximum likelihood. 
     
     
       15. A radio system as claimed in  claim 12 , characterized in that the training sequences ( 404 ,  412 ) of different bursts are overlapped in time domain in each modulation method used by the transmitter. 
     
     
       16. A radio system as claimed in  claim 15 , characterized in that the training sequences ( 404 ,  412 ) which are modulated by different modulation methods and overlapped in time domain are mutually substantially orthogonal, whereby the resolution capacity of different modulation methods increases in the receiver. 
     
     
       17. A radio system as claimed in  claim 12 , characterized in that the means ( 110 ,  210 ) for inferring the modulation method from the impulse response are arranged to use the energy of the impulse response, a signal-to-noise ratio or a signal-to-interference ratio. 
     
     
       18. A radio system as claimed in  claim 12 , characterized in that the receiver is arranged to detect the signal at least partly and means ( 110 ,  210 ) for inferring the modulation method are arranged to utilize the detected portion. 
     
     
       19. A radio system as claimed in  claim 12 , characterized in that the transmitter is arranged to use modulation methods which operate at a different data transmission rate. 
     
     
       20. A radio system as claimed in  claim 19 , characterized in that the radio system is a GSM radio system which is arranged to transmit a FACCH signal, a transmitter FACCH signal is arranged to always transmit at a lower data transmission rate, whereby no FACCH bits are needed in bursts of the modulation methods which operate at higher data transmission rates. 
     
     
       21. A radio system as claimed in  claim 12 , characterized in that the transmitter is arranged to use two modulation methods, of which one is DBCPM enabling a higher data transmission rate and the other is GMSK.